The present invention generally relates to scanning systems capable of reading bar codes. More particularly, the present invention provides a safety feature for detecting low battery voltage.
Some scanning systems of the laser (light amplification by stimulated emission of radiation) type focus a laser beam upon a motor driven, rotating or dithering scanning mirror such that the laser beam forms a scanning pattern across a target bar code. The scanning laser beam is back-reflected to a photodetector, which determines the intensity of the back-reflected laser beam and outputs a current in proportion thereto. Thus a varying signal is output by the photodetector as the laser beam sweeps across a pattern of light and dark "bars" in a bar code.
Control circuitry controls the cooperation and coordination of the components (including the timing) and converts the photodetector output signal into useful form. Scanning speed is chiefly controlled by the speed of the motor.
It is important in prior art scanning systems that the power output of the power supply be kept at an acceptable level so that the scanning system can properly function. Battery power supplies are especially susceptible to depletion and thus power output reduction. Thus, it is desirable to monitor the battery power output, and indicate an unacceptably low output to the scanning system user, so that the battery may be replaced, for example.